Mayor Bloomberg has donned a hardhat countless times as he framed his greatest legacy: the city itself.NY Post composite

New York City comprises five very different boroughs, but Michael Bloomberg dreamed of a single, shimmering metropolis — one of skyscrapers where none stood before; of desolate neighborhoods brought back to life; of moribund waterfronts teeming anew; and of a magical park on a trestle where steam locomotives once delivered beef and grain.

In 12 years, he made much of his vision a reality. “The Bloomberg legacy is going to be part of New York for the next 50 years because he changed the physical landscape,” says NYU urban policy and planning authority Mitchell Moss. “So much of our land was undervalued, and he gave it value.”

That he accomplished it despite the catastrophic economic impact of 9/11, the 2008 Wall Street crash and Hurricane Sandy makes it more remarkable. Unlike Robert Moses, Bloomberg didn’t bulldoze homes. But he wielded a ruthless hand on the levers of mayoral clout, tempered by more respect for the way New Yorkers live, work and play than his numbers-driven techno-speak might suggest.

He brought no particular urban-planning ideology, but only common sense, to the task of remaking New York for the 21st century. Yet it was ferocious common sense, reinforced by a steel will and a $25 billion personal fortune, which freed him from placating special interests.

It will take years, if not generations, to fully perceive what the whirlwind wrought. This is not merely because the changes are many and vast to how neighborhoods and the communities they serve function. The larger imponderable is: How will all the pieces of the puzzle fit together as part of the new urban fabric?

By now, Bloomberg’s credits can sound like old news: nearly 40 percent of city land rezoned, often (although far from always) to allow larger new buildings. Since 2001, 40,000 new structures, 170,000 new housing units, 450 miles of bike lanes, nearly 1,000 acres of new parks.

Or forget statistics and use your eyes. Stand in the middle of Columbus Circle, once a traffic nightmare and camp for the homeless. Time Warner Center was under way before Bloomberg took office, but everything else owes its existence or pristine condition to his administration.

The sparkling Museum of Arts & Design came into being when the city sold off crumbling 2 Columbus Circle. The streamlined traffic flow and landscaped oasis in the circle’s once-forbidding center are a product of the Department of Transportation and other agencies. The radiant restoration of Art Deco 240 Central Park South by its owners followed its 2002 designation as a protected city landmark.

Bloomberg had made his fortune on Wall Street and in technology, and understood those businesses as none of his predecessors did. He had no sentimental attachment to abandoned “manufacturing” districts. Yet City Hall had allowed precious parcels of all five boroughs to remain zoned as if we were still the factory town of 1950.

Bloomberg’s 120 different rezoning measures brought forth new hotels in the dying West 30s, modest commercial regeneration in the Bronx, and modern apartment buildings along the desolate Williamsburg, Greenpoint and Long Island City waterfronts.

His Economic Development Corporation built the great High Line Park. Bloomberg utilized tax benefits and infrastructure investment to get two mighty endeavors off the ground: Hudson Yards, where an 80-story office tower is under way for Coach Inc. and L’Oreal, and Atlantic Yards, where Barclays Center symbolizes the “new” Brooklyn.

Many more grand projects are coming. Among them: the Roosevelt Island $2 billion Cornell-Technion biotech campus and Essex Crossing, a humanely scaled housing, cultural and retail complex on six acres between Delancey Street and Grand Street.

Not every Bloomberg action clicked right out of the gate. Brooklyn’s Fourth Avenue, a backwater of auto repair shops, was rezoned in 2003 to allow new apartment buildings up to 12 stories tall. But the measure neglected to require them to include retail uses. Then the recession stalled some projects before they got off the ground — yielding a staccato procession of boxy, charmless new structures without stores or cafes.

Yet those buildings quickly filled with residents. The city later fine-tuned the zoning to include stores and restaurants, and the delayed ventures are roaring back to life.

In Times Square, too, Bloomberg secured the territory first and left the fine points for later. However popular with tourists, the asphalt pedestrian plazas are unworthy of their iconic location. But a $45 million redesign to replace their schoolyard surfaces with twinkling, light-reflective concrete will make all the difference, judging by the first stage now under way.

Yet, while Bloomberg opened up many precincts to growth, he severely inhibited it in others. This is a less recognized part of his legacy. He imposed fresh limits on construction in more low-rise residential neighborhoods than he up-zoned, from Williamsbridge/Baychester in the Bronx to remote corners of the Rockaways.

Preserving districts where dramatic transformation surely would otherwise have occurred is itself a kind of transformation. Bloomberg’s Landmarks Commission established 32 percent more historic districts — where the panel micro-manages what may be built — than existed before. On the Upper West Side and in the West Village, nearly 70 percent of all buildings are now covered by individual landmark or historic-district protection. Bloomberg the tower- and condo-builder was also the greatest preservationist of them all.

So, again — how will it all play out 10, 20 and 50 years from now?

Will the movement of companies to Hudson Yards towers superior to older ones elsewhere undercut Midtown and Downtown?

Will the appeal of waterfront living in Williamsburg and Hunters Point diminish the desirability of those neighborhoods’ traditional dwelling grounds?

Will the “Skyscraper Historic District” on Brooklyn’s Court Street, which preserved a bunch of weathered old office buildings, prove a boon or a blight to neighboring brownstone communities?

Also, Bloomberg left one piece of crucial unfinished business: his aborted attempt to rezone East Midtown, a “premier” but increasingly obsolescent office district astride Park Avenue where buildings average 70 years old.

He waited until it was too late. So it was cut down in a buzzsaw of “community” resistance over density and infrastructure. But that rare blunder will likely be remedied by Bill de Blasio or his successor.

The myriad gifts Bloomberg bestowed on the cityscape will be remembered more than the one he couldn’t quite deliver. The new New York he made, from Riverdale to Coney Island, is just being born — a hint of the full-blown Bloombubble which our children, and our children’s children, will behold.

FIDI

EPA

The mayor got off to a weak start in Lower Manhattan, at first objecting to commercial reconstruction and ceding control of the area post-9/11 to then-Gov. George Pataki. But one of his first steps in office was crucial: He killed the NYSE’s plan for a 60-story tower in the middle of Wall Street, a project which made no sense in the digital age. That signal from City Hall helped open up FiDi to its residential boom. In 2006, Bloomberg brokered a deal between the Port Authority and Larry Silverstein over new World Trade Center towers that finally allowed major construction to start. He rescued the faltering Memorial with his own funds and by twisting bankers’ arms to pony up as well. City incentives lured a swelling tide of technology companies to older office buildings.

LONG ISLAND CITY WATERFRONT

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In LIC’s Hunter’s Point section, Bloomberg created an entirely new neighborhood along the post-industrial East River waterfront — one of several he set in motion in Brooklyn and Queens. The Economic Development Corp. in 2012 opened the Hunter’s Point South Waterfront Park, a five-acre open space on the full 30-acre site that will eventually boast 5,000 new apartments, 60 percent of them “affordable.” The city spent $66 million to build the park and related infrastructure.

HIGHLINE/CHELSEA

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Bloomberg spared the crumbling old train trestle from demolition (for which permits had been issued) and in 2002 embraced the idea of turning it into a park. The city paid most of its $152 million construction cost and built it. In 2005, Bloomberg rezoned neighboring West Chelsea to exploit the park’s magnetic pull years before it was opened. The moves catalyzed well over $20 billion in new development, much of it in architecturally compelling apartment buildings but also in dramatic adaptive re-uses, such as the Avenues World School in a former grocery warehouse.

BROOKLYN BRIDGE PARK

Brian Zak

Bloomberg was instrumental in creating the public-private partnership behind this 85-acre jewel of greenery at the foot of the bridge and the edge of the thriving and growing Dumbo neighborhood. When completed, it will stretch from the foot of Atlantic Avenue to the Manhattan Bridge. The city contributed about half of the $350 million for infrastructure upgrades on rotting piers and lawns. Bloomberg also stimulated private-sector apartment and hotel projects nearby that will help pay for the park’s upkeep and security.

BARCLAYS CENTER

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Although state condemnation was the prime mover behind Atlantic Yards, the city played a prominent role as well. Bloomberg gave a generous tax subsidy to developer Bruce Ratner. He lent the prestige of his office to the controversial project, which had to overcome years of lawsuits. Rezoning of several neighborhoods around the sports and entertainment mecca liberated them from decades of neglect. Barclays’ arrival inspired a store and restaurant boom on all sides. The world’s tallest prefab apartment tower, now rising behind the arena, is being assembled at the Brooklyn Navy Yard, the former shipbuilding complex that’s now a thriving industrial park thanks to massive city investment under Bloomberg.

A WHEEL DEAL?

Office of the Mayor of New York

The Staten Island Wheel will be a towering testament to Bloomberg’s vision. Rising 625 feet over the St. George waterfront, the elegant, lacy structure would be the world’s tallest Ferris wheel. Scheduled to break ground in 2014 and open in 2016, it’s part of a planned $580 million complex near the ferry terminal to also include a 350,000-square-foot Empire Outlets shopping mall. Both projects received all city approvals. However, the state last week declined to provide an economic development grant to the Wheel, which has a different development team than the Outlets. It wasn’t clear what effect, if any, that decision would have.